I use OPlayer playlists to play background music in my practice (Massage & Wellness). I have the problem that not all the files have been normalized to the same volume. It would be very convenient if I could apply a volume gain per file so the entire playlist would remain close to the same volume.

For example, I have three files in my playlist, SongA, SongB, SongC. SongA is my reference song. SongB is a bit too quite and needs to be +6db to get the volume of SongA. SongC is a tad too loud and I want to adjust it -3dB.

As a bonus an automatic volume normalization, for the playlist, based on perceived volumes (A-weighting) would be awesome!